The recent development of the AVEC methods of video-enhanced microscopy have made it possible to observe and record fast axonal transport of tubulovesicular elements in the axoplasm of large invertebrate neurons. In the giant axon of the squid, extruded axoplasm remains active for hours, making an ideal paradigm for many types of experiments. Thus it is now possible for the first time to design experiments aimed at a comprehensive analysis of the mechanisms of fast axonal transport. We have selected six invertebrate nerve preparations, each having some special features advantageous to this study. The AVEC methods will be used to characterize fast axonal transport in these six preparations and using them test a number of hypotheses regarding the mechanisms of fast axonal transport. Experimental approaches will include motion analysis, pharmacological experiments, the use of cytoskeletal proteins (or derivatives therof), antibodies to cytoskeletal proteins and mechanoenzymes, and metabolic inhibitors to influence fast axonal transport. Efforts will be made to disrupt and fractionate axoplasm under conditions sufficiently mild that motility can be retained by a single fraction or restored to a mixture of two or more fractions. The ultimate goal is to understand the process of fast axonal transport.